Stents, grafts and a variety of other endoprostheses are well known and used in interventional procedures, such as for treating aneurysms, for lining or repairing vessel walls, for filtering or controlling fluid flow, and for expanding or scaffolding occluded or collapsed vessels. Such endoprostheses can be delivered and used in virtually any accessible body lumen of a human or animal and can be deployed by any of a variety of recognized means.
One type endoprosthesis is the stent, which is employed for the treatment of atherosclerotic stenosis in blood vessels. After a patient undergoes a percutaneous transluminal coronary angioplasty or similar interventional procedure, a stent is often deployed at the treatment site to maintain patency of the vessel. The stent is configured to scaffold or support the treated blood vessel and, if desired, may be loaded with a beneficial agent so as to act as a delivery platform to reduce restenosis or the like.
The endoprosthesis is typically delivered by a catheter delivery system to a desired location or deployment site inside a body lumen of a vessel or other tubular organ. To facilitate such delivery, the endoprosthesis must be capable of having a particularly small crossing profile to access deployment sites within small diameter vessels. Additionally, the intended deployment site may be difficult to access by a physician and often involves traversing the delivery system through the tortuous pathway of the anatomy. Therefore, it would be desirable to provide the endoprosthesis with a sufficient degree of longitudinal flexibility during delivery to allow advancement through the anatomy to the deployed site.
Once deployed, the endoprosthesis should be capable of satisfying a variety of performance characteristics. The endoprosthesis should have sufficient rigidity or outer bias to perform its intended function, such as opening a lumen or supporting a vessel wall. Similarly, the endoprosthesis should have suitable flexibility along its length when deployed so as not to kink or straighten when deployed in a curved vessel. Therefore, it would be desirable for the endoprosthesis to provide substantially uniform or otherwise controlled scaffolding of the vessel wall.
Numerous designs and constructions of various endoprosthesis embodiments have been developed to address one or more of the performance characteristics summarized above. For example, a variety of stent designs are disclosed in the following patents: U.S. Pat. No. 4,580,568 to Gianturco; U.S. Pat. No. 5,102,417 to Palmaz; U.S. Pat. No. 5,104,404 to Wolff; U.S. Pat. No. 5,133,732 to Wiktor; U.S. Pat. No. 5,292,331 to Boneau; U.S. Pat. No. 5,514,154 to Lau et al.; U.S. Pat. No. 5,569,295 to Lam; U.S. Pat. No. 5,707,386 to Schnepp-Pesch et al.; U.S. Pat. No. 5,733,303 to Israel et al.; U.S. Pat. No. 5,755,771 to Penn et al.; U.S. Pat. No. 5,776,161 to Globerman; U.S. Pat. No. 5,895,406 to Gray et al.; U.S. Pat. No. 6,033,434 to Borghi; U.S. Pat. No. 6,099,561 to Alt; U.S. Pat. No. 6,106,548 to Roubin et al.; U.S. Pat. No. 6,113,627 to Jang; U.S. Pat. No. 6,132,460 to Thompson; U.S. Pat. No. 6,331,189 to Wolinsky et al.; and U.S. Pat. No. 7,128,756 to Lowe et al., the entireties of which are incorporated herein by reference.
During use, an endoprosthesis is subjected to a variety of stresses and strains due to compressive, bending and torsional forces applied to the endoprosthesis. Current endoprosthesis designs provide only limited resistance to clinical fatigue, sometimes leading to stent fracture after implantation. This problem is particularly acute for endoprosthesis implanted in body portions that subject the endoprosthesis to severe environments, for example, for stents implants in the superficial femoral artery (SFA). A stent implanted in the SFA is subject to bending and torsional forces after implantation, which may cause the stent to eventually fracture. Not only does a fracture cause a loss of scaffolding properties of the stent and a possible puncture of the vessel, but clinical studies have shown a correlation between stent fracture and restenosis.
Therefore, it would also be desirable to provide an endoprosthesis design that not only provides increased axial and torsional flexibility of the endoprosthesis, but that also offers improved resistance to clinical fatigue.